The present application relates to an exterior member for a battery element for packaging a battery element and to a non-aqueous electrolyte secondary battery using the same. In more detail, the present application relates to an exterior member for a battery element capable of reducing failures, for example, leakage of the contents of a battery and swelling of a battery to be caused due to moisture absorption from the outside of the battery, through an enhancement of hermetic sealing properties, and to a non-aqueous electrolyte secondary battery using the same.
In recent years, a number of portable electronic devices, for example, camcorders (video tape recorders), cellular phones and laptop computers, each achieving a reduction in size and weight, have appeared. Following this, a demand for batteries as a power source of portable electronic devices is rapidly increasing. In order to realize a reduction in size and weight of the device, it is demanded to design the battery such that the battery is lightweight and thin and that a housing space within the device can be efficiently used. As a battery capable of meeting such demands, a lithium ion battery with a large energy density and a large output density is the most favorable.
Above all, a battery with a high degree of freedom in shape, a sheet type battery with a thin large area, a card type battery with a thin small area and the like have been desired. However, it is difficult to prepare a thin battery according to techniques using a metal-made can as an exterior material, which have hitherto been employed.
In order to solve these problems, there are investigated batteries not containing a liquid electrolyte therein, by adding a material having a solidification action to an electrolytic solution or using a gel electrolyte using a polymer. In such batteries, an electrode and an electrolyte are brought into intimate contact with each other, and it is possible to keep the contact state. According to this, it is possible to prepare a thin battery using an exterior member in a sheet form, such as an aluminum laminated sheet.
FIG. 9 shows an exploded perspective view of the foregoing thin battery using a laminated sheet as an exterior member. This laminated battery 10 is configured such that a battery element 20 is externally packaged in an exterior member 30 for a battery element made of a laminated sheet.
Here, the exterior member 30 for a battery element is formed such that a recess-provided sheet piece 30A having a recess 20 for housing the battery element 20 in a rectangular plate form and a platy sheet piece 30B in a platy form are partitioned from each other by a bending part 34. The laminated battery 10 is prepared by housing the battery element 20 in the recess 32 of the recess-provided sheet piece 30A, folding double the recess-provided sheet piece 30A and the platy sheet piece 30B in the bending part 34 and then sealing a peripheral part 36 of the both sheet pieces under a heat pressure.
The foregoing bending part of the laminated sheet is bent at about 360° C. during sealing and further applied with a load of the heat pressure. Thus, the bending part of the laminated sheet is easily damaged at the time of sealing as compared with other peripheral part (sealing part). Nevertheless, according to the related art, since a sealing region (peripheral part width) of the laminated sheet was sufficiently secured, even when the foregoing load would be applied, the damage was rarely actualized. However, in recent years, following an increase of the battery capacity, not only the sealing region is made narrow to a minimum width, but in order to compensate this, there is a tendency that sealing is carried out at high temperature and high pressure. Accordingly, the foregoing bending part forms a place where delamination or a pinhole which will become a factor of lowering the hermetic sealing properties is easily generated. Thus, it is the present situation that there is a concern that a lowering of the hermetic sealing properties of the thin laminated battery is generated.
On the other hand, there is disclosed a method in which one of external ends of a laminated exterior body is extended to provide an extended end, and the other external end is covered by the extended end, thereby enhancing hermetic sealing properties (see JP-A-2003-242942).